Trucks and other heavy and medium duty capacity vehicles require a heavy duty or medium duty transmission in the powertrain. The powertrain may include an auxiliary transmission connected to the transmission in order to provide sufficient gearing for a vehicle for additional gear reduction for in powertrain. The user is required to estimate the extent of the torque limiting while using an auxiliary transmission in reduction mode. Reduced drivability or damage to the driveline components may result if the torque nears or exceeds the driveline limits while the auxiliary transmission is in a reducing gear.
An automatic transmission that uses a fixed driveline ratio may lead to poor launch and shift performance when used with an auxiliary transmission.